1. Technical Field
The present invention relates to a toner for electrostatic image development used in forming an image by electrophotography, an electrostatic image developer and an image forming method using the same.
2. Related Art
In electrophotography, an electrostatic image is formed on a photoreceptor (latent image carrier) through a process of charging and light exposure, the electrostatic latent image is developed by a developer containing a toner to form a toner image, and this toner image is transferred onto a recording medium and fixed to form an image. As the developer used herein, there are two-component developers of a toner and a carrier, and one-component developers using either a magnetic toner or a nonmagnetic toner. Production of the toner generally uses a kneading milling process including melting and kneading a thermoplastic resin with a pigment, a charge controlling agent, and a releasing agent such as wax, then cooling the mixture, pulverizing it and further size classifying the particles.
With respect to the toner produced by the conventional kneading milling process, the shape of the toner particle is indefinite, and the surface structure of the toner particle is changed subtly depending on the pulverizability of the materials used and conditions in the milling process, thus making it difficult to systematically regulate the shape and surface structure of the toner particles.
On the other hand, recently a method of producing a toner by wet processes is proposed as a means capable of systematically regulating the shape and surface structure of the toner. Among wet processes, there are wet globularization methods capable of shape regulation, suspension particle formation methods capable of regulating the surface composition, suspension polymerization methods capable of regulating an internal composition, and emulsion polymerization aggregation methods.
As demand for energy saving is increased, there is need for energy saving in the fixation process that uses a certain amount of electric power in a copier, and for reducing the fixation temperature of toner in order to enlarge the fixation region. Reduction in the fixation temperature of a toner enables reduction in waiting time until the fixation temperature of the surface of a fixation roll is reached after inputting electric power to a copier etc., that is, reduction in warm-up time, as well as long life of a fixation roll, in addition to the energy saving and enlargement of fixation region.
Reduction in the fixation temperature of a toner brings about reduction in the glass transition point of the toner causing a problem of deterioration in the storage stability of the toner, and thus it is difficult to get a reduction in the fixation temperature together with storage stability of the toner. To satisfy both fixability at low-temperature and toner storage stability, the toner should have “sharp” melting properties, by which the glass transition point of the toner remains at a high temperature while the viscosity of the toner rapidly reduces at the high-temperature region.
However, the glass transition point and molecular weight of resin used in toners usually have a certain range of variation, and to attain sharp melting properties, the composition and molecular weight of resin need to be closely regulated. For obtaining such a resin, since the molecular weight of the resin needs to be regulated by using a special process or by subjecting the resin to chromatography, is significantly increases the production cost of the resin, and in such processes unrequired resin is formed as a byproduct. That is not preferable from an environmental viewpoint.